Report from –
Andrew Pearson

11/11/2014

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Developer R-Gen, a low energy building specialist, was appointed by Eastlands Homes to deliver one of the largest Passivhaus retrofit projects undertaken by a housing association in the UK. The project was to retrofit to Passivhaus EnerPhit standard, two 1960s blocks, totalling 32 walk-up maisonette-style flats along with six bungalows at Erneley Close, Longsight, Manchester.

Description

“As a developer, I’ve promoted the PassivHaus Standard to housing associations on the basis that affordable housing is not simply about the rent but a home’s running costs too,” says Phil Summers, co-owner of R-Gen Developments.

He says the advantage of Passivhaus is that it is a proven methodology that “guarantees fuel bills are reduced by 80-90%” from those of a traditional, Building Regulations-compliant house. Passivhaus buildings also have low carbon emissions. However, one of the biggest advantages Summers explains is that they Passivahaus buildings deliver better air quality and room temperatures which he says can be a major benefit to residents’ health and can lead to reduced healthcare costs.

The two four-storey blocks of walk-up flats – one containing 12, the other 20 maisonettes – have apartments spread over two floors. The blocks are supported on a frame of reinforced concrete slabs, with each apartment slotted into its individual concrete Pidgeon-hole. The apartments have an external cavity wall with a brick/tile outer leaf inset with uPVC windows. The blocks are topped with a concrete tile, pitched roof.

Summers says it was soon apparent that the footprint of the bungalows was “too big to meet the Passivhaus Planning package requirements”. The flats, however, were suitable for a low energy retrofit.

(Image: R-Gen)

Key Features

The initial strategy was to take down the outer leaf of the cavity wall, which had a significant number of thermal bridges and was in a poor state of repair. With the outer leaf removed the plan then was to add a parge coat to the inner leaf to improve its airtightness and apply 300mm of insulation from the outside. Finally the new façade was to be finished with cladding of Rockpanel Chameleon panels.

The plan had to be abandoned at the outset, when removal of the outer wall revealed the inner leaf in terrible condition. “When we took down the outer wall we found an inner leaf made of rubble, clinker and bits of timber; it had lots of holes and was in fact an unsafe structure,” Summers says. “There were flaws with the building that you wouldn’t be aware of unless you’d emptied the flats and undertaken extensive opening up works,” he adds.

The solution was to decant the tenants so that the entire external wall could be removed and replaced with an insulated timber framed infill panel. This was made airtight inside the flat. Additional works were also needed to the party walls which also leaked air. “It was quite a challenge for the contractor to get the building airtight,” Summers says. However, the scheme eventually passed the Passivhaus airtightness test, with less than one air change per hour at 50Pa.

To ventilate the airtight flats, individual Mechanical Ventilation Heat Recovery units were installed to remove stale air from the bathroom and kitchen and to introduce tempered fresh air to the other rooms. The air tight building and energy efficient ventilation system ensure the building has a space heat demand of less than 25kWh/m2/y.

In addition, the gas supply to the individual flats was decommissioned and communal boilers were installed to provide energy-efficient hot water and heat. The building’s pitched roof was also replaced.

Externally, the building has been ‘rebranded’ using the Rockpanel Chameleon cladding panels, so that it appears to change colour depending on the angle from which it is viewed and the extent of natural light

Lessons learned by the contractor

John Hyland of contractor The Casey Group

The contracts manager, site manager, air tightness champion and specific trades’ foremen need to have been on the Passivhaus Introduction Course and at least one member of the team should have been on the Certified Tradesman Course.

The airtightness champion should be site-based.

Sufficient resources should be made available to monitor aspects of Passivhaus construction such as insulation, cold bridging details and airtightness and ensure supervisors are covered during holidays and periods of illness by suitably trained staff.

The completion of the test and inspection sheets and photography of the various phases is time consuming but important.

For the installation of tapes and membranes: choose carefully those tasked with this work; ensure work areas are clean and dry, use surface cleaners before applying tapes; and concentrate on awkward areas such as junctions and changes of direction.

Choose the external specialist airtightness engineer based on experience and knowledge rather than price

If anything is unclear ask – don’t assume

Aim for better than the minimum one air-change-per-hour target

Carefully consider at design stage how air leakage routes can be sealed, for example in party walls, between floors around electrical sockets.